Certain solenoid valves are required to comply with rather rigid functional specifications. An example of a solenoid valve of this type is found in an automotive vehicle ABS brake system. A typical three-way ABS solenoid valve is required to exhibit close compliance with a specified opening time, a specified closing time, specified seat leak rates for both energized and de-energized conditions, and specified flow rates for both energized and de-energized conditions. It is also typical practice to subject each solenoid valve to testing for assuring compliance with these specifications.
Since ABS solenoid valves are required to handle automotive brake fluid when they are in use, it had been a typical practice to functionally test each valve using either brake fluid itself or some sort of equivalent liquid fluid. When brake fluid itself was used for the testing medium, the testing was particularly expensive. Not only is brake fluid itself costly, but it also requires special handling equipment because of its inherent chemical properties. Typically, mechanical test equipment must be fabricated from stainless steel since brake fluid contact tends to remove paint and degrades most plastics. Electrical wiring had to be teflon-coated in order to resist damage. Because brake fluid is also hydroscopic, it tends to promote rust as well. Because of these factors, it would be especially beneficial if the solenoid valves could tested in dry air rather than in wet liquid. Others have attempted to develop apparatus and methods for the dry air testing of the solenoid valves, but it is believed that at most only limited success has been achieved. To the extent that others may actually be performing dry air testing of this type of solenoid valve, it is believed that such testing is conducted using very high air pressures, for example greater than 14 Bar. The use of such high air pressures requires relatively more expensive test equipment and the use of such high air pressures is a potential source of danger if care is not taken.
The present invention relates to new and unique test apparatus and methods for testing solenoid valves in dry air at comparatively low pressures in a manner that reliably correlates the dry air test results with results that would be obtained by equivalent testing using liquid media such as brake fluid. Thus, the disadvantages that are associated with the wet testing of solenoid valves, as described above, can be avoided. This in turn yields meaningful economies in the mass production of solenoid valves.
One aspect of the invention relates to apparatus and method for the pressure decay testing of solenoid valves in air which correlates with extremely small leak rates of brake fluid at a very high pressure differential, such as a 138 Bar pressure differential.
Another aspect of the invention relates to measurement of the on and off response times of the solenoid valve and incorporates an accelerometer that is mounted on the valve test fixture for detecting the initial seating of the valve element on a valve seat in response to respective energization and de-energization of the solenoid valve. A further aspect of the invention relates to apparatus and method for the flow rate testing of the solenoid valve by utilizing orifices and pressure transducers in particular configurations with the valve under test.
Although the present description of the invention is given for the testing of a particular three-way ABS solenoid valve, it is to be appreciated that the inventive principles may be applied to the testing of other types of high performance solenoid valves.
The foregoing features, advantages and benefits of the invention will be seen more fully in the ensuing description and claims. Drawings accompany the disclosure and illustrate a preferred embodiment of the invention according to the best mode contemplated at the present time for carrying out the invention.